The subject invention is generally directed to phase inverting baluns, and is directed more particularly to a phase inverting balun structure that operates over a multi-octave bandwidth.
Phase inverting baluns are two-way power dividers with anti-phase outputs that are commonly utilized in a variety of feed networks ranging from cable TV applications to radar and array antenna applications. A known phase inverting balun for radar applications comprises a Magic Tee, or a stripline version of the waveguide device (a 180 degree hybrid coupler). The two ports provide two anti-phase signals. Conventionally, the 180 degree output is achieved by using a 90 degree quadrature hybrid plus a 90 degree phase shifter, or by inserting a delay line in one of the two arms with respect to the other. Either way, it is difficult to achieve the phase inversion over a multi-octave bandwidth. Other designs also provide band limited performance.
"Broadband Stripline Balun Using Quadrature Couplers," IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, February 1968, pages 132-133 and "The Balun Family," Shuhao, MICROWAVE JOURNAL, September 1987, pages 227-229, include examples of known phase inverting balun designs.
In addition to band limited performance considerations, known baluns structures that presently have the widest bandwidths are complex and expensive.